There appears to be two alternatives as to scratch origin. Either the scratch was present before peening or it was imposed after peening. If it was present before peening then the scratch cannot be sharp and must have appear to have been 'blurred' by the action of peening. If the scratch appears to be sharp, then it must have occurred after peening - as a result of part handling. A blurred scratch is rare but can be the result of a scratch having been smoothed over by a burnishing type of process applied prior to peening. During burnishing metal flows over the scratch hiding it from view. Subsequent peening then stretches the surface revealing a (blurred) scratch.
